1. Field of the Invention
The present invention relates to a mobile telephone terminal which is driven by a battery, particularly a mobile telephone terminal which can considerably reduce power consumption in order to extend the life of the battery.
The mobile telephone terminal of the present invention can be applied to variety of mobile telephone terminals operated under a cellular system, such as a land mobile radio telephone, a shoulder type radio telephone, a portable type radio telephone and so on. The land mobile radio telephone and shoulder type radio telephone are substantially the same belonging to class I, producing a transmitting power of, for example, 3 W. The portable type radio telephone belongs to class III producing a transmitting power of, for example, 0.6 W.
2. Description of the Related Art
Especially, in the technical field of a battery feed type mobile telephone terminal, it is desired to reduce power consumption as much as possible to extend the life of the battery.
In general, a mobile telephone terminal is constructed to use a microcomputer. This is because, the mobile telephone terminal requires a variety of complicated processes to be carried out therein. Further, it is preferable to use a microcomputer from the viewpoints of convenience in constructing the mobile telephone system, economy in building the system, and minimizing the scale thereof.
As for the microcomputer, usually an 8 bit main central processing unit (CPU) and a 4 bit sub CPU are used. The main CPU handles terminal control, data reception processing, data transmission processing, timer management and so on. On the other hand, the sub CPU handles man-machine communication processes, such as a process of driving a display mounted on the mobile telephone terminal, a process of an operating of keys which are also mounted thereon. Further, the mobile telephone terminal requires, other than the above, base band processing, transmitting and receiving processing, and the like.
As mentioned first, in the battery feed type mobile telephone terminal, it is desired to reduce power consumption as much as possible. For this, the circuits for constructing the mobile telephone terminal, including the above-mentioned main and sub CPU's, are realized by complementary metal-oxide-semiconductor (CMOS) devices. As known, the CMOS device is a low power consumption device.
The CMOS device is a low power consumption type device, but current flows therethrough every time an ON-OFF operation is performed therein, so that power supplied from the battery becomes large. As known, the frequency of the ON-OFF operations is proportional to an operating speed, or operating frequency of the CMOS device. Therefore, the power consumption is relatively large at the main CPU and memories, such as a read only memory (ROM) and a random access memory (RAM), cooperating with the main CPU, since the main CPU and the memories work at a relatively high operating frequency, for example, 1 MHz or 2 MHz.
Thus, a problem resides in that a large amount of power supplied from the battery is needed by the main CPU, ROM, and RAM as long as these are operated at a high operating frequency. This apparently shortens the life of the battery.